Um infusor autônomo para um expansor de pele subcutâneo / An autonomous infuser for a subcutaneous skin expander

Introdução: A expansão da pele é um processo fisiológico definido como a capacidade de aumentar sua área superficial em resposta a uma tensão ou a uma dada deformação. Para realizar a cirurgia reconstrutiva, os expansores de pele são implantados sob a pele e periodicamente infiltrados com uma solução salina para fornecer um retalho extra de pele. Quando o volume interno prescrito do expansor é alcançado, a cirurgia reconstrutiva é realizada. Métodos: Foi desenvolvido um dispositivo semiautomático e portátil para facilitar um procedimento de expansão da pele. O dispositivo tem como objetivo simplificar o processo de infiltração, proporcionando mobilidade e independência para o paciente, e assegurando ao médico a qualidade e a precisão das infiltrações realizadas. O dispositivo também permite expansão contínua em pacientes hospitalizados. Resultados: Usando um código, o médico tem acesso ao menu do dispositivo e define a pressão máxima e/ou o valor máximo para cada expansor do paciente. O paciente pode realizar a infiltração e ter acesso ao controle da velocidade de infiltração, reverter ou parar a operação. Todos os dados são gravados em um SIM Card e incluem data, hora, volumes inicial e final, e pressão inicial e final de cada procedimento para cada expansor. Conclusões: O dispositivo automatiza e otimiza a expansão, de modo que o que o médico possa prescrever um limite para cada expansão, seja uma pressão máxima ou voluma infiltrado. Todos os dados são gravados, fornecendo um importante banco de dados sobre o comportamento de pele relacionado a gênero, raça, idade e local da expansão.

Introduction: Skin expansion is a physiological process defined as the ability of human skin to increase its superficial area in response to a stress or given deformation. In reconstructive surgery, skin expanders are implanted beneath the skin and periodically infiltrated with a saline solution to provide an extra flap of skin. When the prescribed internal volume of the expander is reached, reconstructive surgery is performed. Methods: A semiautomatic and portable device was developed and built to facilitate a skin expansion procedure. The device aims to simplify the infiltration process, providing mobility and independence to the patient and assuring the physician of the infiltration quality and precision. The device also enables continuous expansion in hospitalized patients. Results: Using a code, the doctor accesses the menu of the device and sets the maximum pressure and/or value for each expander of the patient. The patient can control the infiltration velocity and reverse or stop the operation. All data are recorded on a simcard and include date, time, initial and final volumes, and initial and final pressures of each procedure for each expander. Conclusions: The device motorizes and optimizes the expansion, allowing the doctor to prescribe a maximum infiltration pressure or volume. All data are recorded to provide an important database of skin behavior related to sex, race, age, and expansion site.

A 'cheap' optimal control approach to estimate muscle forces in musculoskeletal systems.

This paper shows a new method to estimate the muscle forces in musculoskeletal systems based on the inverse dynamics of a multi-body system associated optimal control. The redundant actuator problem is solved by minimizing a time-integral cost function, augmented with a torque-tracking error function, and muscle dynamics is considered through differential constraints. The method is compared to a previously implemented human posture control problem, solved using a Forward Dynamics Optimal Control approach and to classical static optimization, with two different objective functions. The new method provides very similar muscle force patterns when compared to the forward dynamics solution, but the computational cost is much smaller and the numerical robustness is increased. The results achieved suggest that this method is more accurate for the muscle force predictions when compared to static optimization, and can be used as a numerically 'cheap' alternative to the forward dynamics and optimal control in some applications.

Moment arms and musculotendon lengths estimation for a three-dimensional lower-limb model.

This paper presents a set of polynomial expressions that can be used as regression equations to estimate length and three-dimensional moment arms of 43 lower-limb musculotendon actuators. These equations allow one to find, at a low computational cost, the musculotendon geometric parameters required for numerical simulation of large musculoskeletal models. Nominal values for these biomechanical parameters were established using a public-domain musculoskeletal model of the lower limb (IEEE Trans. Biomed. Eng. 37 (1990) 757). To fit these nominal values, regression equations with different levels of complexity were generated, based on the number of generalized coordinates of the joints spanned by each musculotendon actuator. Least squares fitting was used to identify regression equation coefficients. The goodness of the fit and confidence intervals were assessed, and the best fitting equations selected.

Biomechanical modeling and optimal control of human posture.

The present work describes the biomechanical modeling of human postural mechanics in the saggital plane and the use of optimal control to generate open-loop raising-up movements from a squatting position. The biomechanical model comprises 10 equivalent musculotendon actuators, based on a 40 muscles model, and three links (shank, thigh and HAT-Head, Arms and Trunk). Optimal control solutions are achieved through algorithms based on the Consistent Approximations Theory (Schwartz and Polak, 1996), where the continuous non-linear dynamics is represented in a discrete space by means of a Runge-Kutta integration and the control signals in a spline-coefficient functional space. This leads to non-linear programming problems solved by a sequential quadratic programming (SQP) method. Due to the highly non-linear and unstable nature of the posture dynamics, numerical convergence is difficult, and specific strategies must be implemented in order to allow convergence. Results for control (muscular excitations) and angular trajectories are shown using two final simulation times, as well as specific control strategies are discussed.